1. Field of the Invention
The present invention relates to a production process of a color filter, comprising applying inks by an ink-jet system to form colored portions, a liquid crystal display device using the color filter produced by the production process, and an ink-jet head.
2. Related Background Art
With the advancement of personal computers, particularly, portable personal computers in recent years, the demand for liquid crystal display devices, particularly, color liquid crystal display devices tends to increase. It is however necessary to reduce the cost of the color liquid crystal display devices for further spreading them. There is an increasing demand for reduction in the cost of color filters particularly given much weight from the viewpoint of the cost.
Various methods have heretofore been attempted for meeting the above demand while satisfying properties required of the color filters. However, no method satisfying all the required properties is yet established. The individual methods will hereinafter be described.
The first method oftenest used is a dyeing process. In the dyeing process, a layer of a water-soluble polymeric material, which is a material to be dyed, is first formed on a glass substrate, and the layer thus formed is patterned in the desired form by a photolithographic step. Thereafter, the substrate on which the coating film has been patterned is immersed in a dye bath to obtain a colored pattern. These steps are repeatedly performed three times to produce a color filter layer composed of colored patterns of red (R), green (G) and blue (B).
The second method is a pigment dispersing process which has been replacing the dyeing process in recent years. In this process, a layer of a photosensitive resin in which a pigment has been dispersed is first formed on a substrate and then subjected to patterning, thereby obtaining a pattern of a single color. These steps are repeatedly performed three times, thereby producing a color filter layer composed of colored patterns of R, G and B.
As the third method, there is an electrodeposition process. In this process, a transparent electrode is first patterned on a substrate. The substrate is then immersed in an electrodeposition coating fluid containing a pigment, a resin, an electrolytic solution and the like to electrically deposit the first color. These steps are repeatedly performed three times, thereby forming a color filter layer composed of colored patterns of R, G and B. Finally, this color filter layer is baked to produce a color filter.
The fourth method is a process which comprises the steps of applying three times separately resin dispersions of R, G and B colors prepared each by dispersing a pigment having respective colors into a thermosetting resin, and then thermosetting the resin portions thus applied to form a colored layer. It is general to form a protective layer on the colored layer in each process.
The need of repeating the same steps three times to form the three colored patterns of R, G and B is common to these processes. Therefore, the production cost is necessarily increased. There is also offered a problem that a yield is reduced as the number of steps increases. Further, in the electrodeposition process, formable patterns are limited. It is hence difficult to apply this process to an active matrix type color liquid crystal display device using TFT (thin layer transistor), what is called TFT type color liquid crystal display device, in the existing technique. Further, the printing process is poor in resolution and is hence unfit for the formation of fine-pitch patterns.
In order to compensate the above-described drawbacks of the conventional production processes, Japanese Patent Application Laid-Open Nos. 59-75205, 63-235901, 1-217302 and 4-123005 each have proposed a process for producing a color filter using an ink-jet system. These processes are different from the above-described conventional processes. In these processes, respective inks of R, G and B colors are applied to prescribed positions on a transparent substrate by an ink-jet head, and the inks thus applied are dried on the substrate to form colored portions. According to these processes, the formation of the individual colored patterns of R, G and B can be performed at once, and moreover the amount of the inks to be used is saved. Therefore, they have effects of enhancing productivity to a great extent and reducing the cost.
The present applicants have previously proposed, as a production process of a color filter using an ink-jet system, a process in which a coloring region is divided into plural scanning regions in order to color the wide coloring region, and the respective scanning regions are successively colored due to moving an ink-jet head, as described in Japanese Patent Application Laid-Open No. 9-138306. In this process, color unevenness has been easy to occur in the vicinity of boundaries between the scanning regions. Therefore, coloring conditions have had to be severely controlled so as not to cause color unevenness. The present applicants have also proposed a process in which scanning for coloring is conducted plural times in the same scanning region, and the position of an ink-jet head is shifted in each scan for coloring, whereby each colored portion is formed with an ink ejected from a plurality of nozzles. The specific coloring process of this proposal will be described by specific examples illustrated in FIGS. 14, 15A to 15C and 16A to 16C. Incidentally, a color filter is generally produced by successively arranging 3 colored portions of R, G and B. For convenience"" sake, however, a description is given by illustrating a state that colored portions of the same color have been arranged.
As illustrated in FIG. 14, a coloring region on a substrate 1 on which a color filter will be formed is first divided into a plurality of scanning regions 90a to 90f according to the length of an ink-jet head 2 having a plurality of nozzles 3. FIGS. 15A to 15C illustrate an example where the scanning regions 90a to 90c each composed of 6 coloring portions 11 are colored by the ink-jet head 2 having 8 nozzles 13a to 13h. The ink-jet head 2 is first set in such a manner that the nozzles 13a to 13f correspond to the respective coloring portions 11 of the scanning region 90a located at a left end of the coloring region to intermittently eject ink droplets to the coloring portions 11 from the respective nozzles 13a to 13f while scanning the ink-jet head 2 in the longitudinal direction of each coloring portion 11 in a state that the ejection of an ink from the nozzles 13g and 13h has been suspended (FIG. 15A).
The ink-jet head 2 is then shifted by a distance corresponding to one nozzle, and a second scan is conducted in a state that the ejection of the ink from the nozzles 13a and 13h has been suspended, so as to intermittently eject ink droplets to the coloring portions 11 from the nozzles 13b to 13g (FIG. 15B).
The ink-jet head 2 is further shifted by a distance corresponding to one nozzle, and a third scan is conducted in a state that the ejection of the ink from the nozzles 13a and 13b has been suspended, so as to intermittently eject ink droplets to the coloring portions 11 from the nozzles 13c to 13h (FIG. 15C).
The scanning for coloring the scanning region 90a is completed by the above-described 3 scans. As illustrated in FIGS. 16A to 16C, scanning for coloring is subsequently conducted plural times on the scanning region 90b while shifting the nozzles used one by one in the same manner as in the scanning for coloring in the scanning region 90a. In FIGS. 16A to 16C, reference numerals 107 marked with xe2x80x9c{circle around (xe2x88x92)}xe2x80x9d and 108 marked with  designate ink droplets applied to scanning regions 90a and 90b, respectively. Scanning region 90c in FIGS. 16A to 16C will be colored similarly as above.
In the above-described manner, the ink droplets ejected from the plurality of nozzles are applied to the respective coloring portions, whereby color unevenness due to ejection irregularity among nozzles can be mitigated.
However, when such a process as illustrated in FIGS. 14, 15A to 15C and 16A to 16C is used, stripe-like color unevenness is liable to be observed in the vicinity of boundaries between the adjacent scanning regions, though color unevenness in the same scanning region is mitigated.
As the cause that color unevenness is easy to occur in the vicinity of boundaries between the adjacent scanning regions in the coloring process illustrated in FIGS. 14, 15A to 15C and 16A to 16C, it is considered that colored portions in the vicinity of the boundaries (boundary areas) are different from colored portions in the center of each scanning region in the following points.
(1) There is a great time lag when coloring portions at the boundary areas in the regions different from each other are colored.
(2) Since the positions of nozzles that apply an ink to the coloring portions at the boundary areas are greatly distant from each other in the ink-jet head (nozzles located at both ends), differences in physical quantities such as quantities of ink droplets ejected and impact positions of the ink droplets between such nozzles are liable to be greater than those between adjoining nozzles.
It is an object of the present invention to provide a production process of a color filter, by which a high-quality color filter free of color unevenness can be produced through simple steps by an ink-jet system, a liquid crystal display device using the color filter produced by this production process, and an ink-jet head used in this production process.
The above object can be achieved by the present invention described below.
According to the present invention, there is thus provided a process for producing a color filter, comprising the steps of dividing a coloring region on a substrate into a plurality of scanning regions and successively coloring the respective scanning regions by an ink-jet system, wherein the scanning regions have a portion overlapped each other.
According to the present invention, there is also provided a liquid crystal display device comprising a color filter substrate produced by the production process described above, an opposite substrate arranged in an opposing relation to the color filter substrate, and a liquid crystal enclosed in a space between both substrates.
According to the present invention, there is further provided an ink-jet head having a plurality of nozzles, wherein a difference in ejected ink quantity between nozzles located at both ends of the ink jet head is 20% or less.